The use of metal sheathed heaters is known in the art. Typically, these heaters use resistance heating wherein a resistance heating wire or heater cable is encased in a metal sheath. The metal sheath is in contact with the item or material to be heated. These heaters are often referred to as belly-band, crankcase, compressor, sump heaters and the like. A heater is used to heat refrigeration compressors or air-conditioning compressors. The heater can employ a standard hose clamp or other type of clamping arrangement for attachment to a compressor. The standard hose clamp is cut in two pieces with each piece affixed (welded for example) to opposite ends of the heater's metal sheath.
Assembly of the heater to the compressor is accomplished by engaging the two ends of the clamp as intended and then tightening the assembly around the selected compressor location. This type of heater construction can also be used for heating containers such as barrels, heating pipes, and the like.
The belly-band heater has an insulated electric lead wire exiting at each end of the metal sheath. A frequent requirement in the use of these heaters is for the lead wires to be routed in standard metal conduit. Further, it is often desired that the conduit encloses the lead wires from the point where each lead exits the heater sheath to where the lead wires enter an electrical junction box or boxes.
FIG. 1 shows a typical metal sheathed heater or electric belly-band heater designated by the reference numeral 10 and including hose clamp pieces 1 and 3, and a screw mechanism 5. A metal sheath 7 extends between the two pieces 1 and 3, with the hose clamp pieces attached to the sheath by welding or the like. The metal sheath 7 encases an electrically insulated resistance heating wire or heater cable 9 and includes a fluted strip portion 8, which interfaces with the equipment or material requiring heating.
In these types of metal sheathed heaters, it is known in the industry that the heater cable is composed of resistance wire configured to be spiraled around a flexible core made of an electrically insulated and thermally resistant material, such as fiberglass or other suitable material. This element is commonly referred to as a “heater core wire”. After the heater core wire is uniformly coated with an insulating material having sufficient mechanical and electrical resistance properties so as to remain flexible yet electrically isolated, it may be referred to as a “heater cable”. The insulating material is often silicone or a thermosetting plastic with adequate thermal properties for its intended use.
In connecting the heater cable to the lead wires, a small length of insulation is stripped from each end of the heater cable. Two flexible electrically insulated stranded lead wires with a small length of insulation stripped from one end of each wire are electrically connected, one to each end of the heater cable, by crimping or splicing the stripped ends of the heater cable to stripped ends of the lead wires.
The connector used is a properly selected metal splice connector with sufficient temperature resistance, corrosion resistance, mechanical strength and formability to make a secure electrical bond. Referring to FIG. 1, the lead wires 11 are connected to the heater cable using connections that are in turn encased in the metal sheath as is disclosed in published patent application Ser. No. 2005/0194377 to Kirby, owned by the assignee of this application. The connection between the lead wires and heater cable can be made outside the metal sheath if so desired.
These types of heaters, for example, are disclosed in U.S. Pat. No. 6,844,531 to Kirby, which is herein incorporated in its entirety by reference. Another feature of these types of heaters is a special lead wire joining technique and thermostat arrangement, which are found in the above-mentioned published patent application Ser. No. 2005/0194377 as well as published patent application Ser. No. 2006/0191904 to Kirby, each incorporated by reference herein in their entirety.
Electric resistance compressor heaters, when installed on a compressor that is part of a total system or controlling unit, remain constantly powered regardless of conditions as long as the controlling unit that the heater serves demands power. During certain periods, conditions occur for which the electric resistance compressor heater does not need to operate even though the controlling unit demands power. As a result electrical energy is consumed, which wastes resources and increases energy costs. The use of positive temperature coefficient resistance heaters for heating compressors only partially reduces the use of electrical energy and is not a solution to this problem. Thus, there is a need for improved control of the operation of the types of heaters disclosed above.
Solid-state controls that work in conjunction with sensors (for example temperature sensors) to regulate the power delivered by a heating system are known. Such devices are available on a commercial basis. However, there are no solid-state devices known for controlling electric compressor heaters that monitor conditions and then in turn either switch the heater off and then on again or modulate the power output of the heater to match requirements.